I've successfully connected Lightning to an Outlook.com calendar using the iCalender (ICS) protocol. However, when I try to delete an event from Thunderbird/Lightning, I get this message: Error Code: MODIFICATION_FAILED Description: If you're seeing this message after snoozing or dismissing a reminder and this is for a calendar you do not want to add or edit events for, you can mark this calendar as read-only to avoid such experience in future. To do so, get to the calendar properties by right-clicking on this calendar in the list in the calendar or task view. And under Edit > Calendar Properties, "Read Only" becomes re-checked. If I uncheck it again and attempt to delete an event, I get the above message again (and the event does not delete). So how can I successfully delete events in Lightning?